Recently, a light-emitting diode (LED) light tube has been developed and has become popular as a replacement of a fluorescence light tube, because of its low power consumption and long life characteristic. FIG. 1 shows a configuration of a conventional LED light tube. The LED light tube 100 includes a plurality of LEDs 101 and a printed circuit board (PCB) 103 on which the plurality of LEDs 101 are disposed. An aluminum tube cover 105 constitutes a bottom half of the LED light tube and a transparent plastic tube cover 107 constitutes a top half of the LED light tube. The LED light tube 100 further includes an LED driver circuit 109 that is typically located underneath the PCB 103, and two end-caps 111 with bi-pins 113 for electrical contact.
FIG. 2 shows a cross sectional view of the conventional LED light tube 100 as shown in FIG. 1. The PCB 103 is slotted into grooves 121 formed on the inside of the tube, for example, inside of the aluminum tube cover 105. As shown in FIG. 2, the LEDs 101 are upwardly disposed so that light emitted from the LEDs 101 directly reaches the transparent plastic tube cover 107 and passes through the transparent plastic tube cover 107 to outside of the LED light tube 100.
In the above configuration of the conventional LED light tube, however, “glare” becomes one of the problems. Glare is caused when a bright light source appears in the foreground, superimposed on the background with lower brightness. Since the eyes are initially adapted to the background with low brightness, contrast against the bright light source generates vision discomfort or vision disability to the eyes.
FIG. 3 shows the glare caused by a lamp 131, e.g., a fluorescent lamp tube or bulb, with a shade. To reduce the glare in a conventional light source, a lamp shade 133 or a louver 135 has been used to provide a sharp cutoff angle from the bulb or tube. The cutoff angle “a” is frequently set to cut off the light sharply from 45 degrees upwards. At position 1 of FIG. 3, the observer 137 from afar is shielded from the bulb by the shade 133, and at position 2, as the observer 137 approaches nearer to the cutoff angle “a”, the observer 137 suddenly sees the bulb directly. At position 3, the observer 137 experiences the direct glare if the observer 137 deliberately tilts the head up while walking underneath the lamp 131. When the conventional LED light tube having the transparent cover as shown in FIGS. 1 and 2 is used as the lamp 131, the light emitted from the LEDs will be more visible from afar than the lamp with a shade or louver, even at a near horizontal angle, causing discomforting glare.
To overcome the glare problem, the conventional LED light tube has utilized a semi-transparent plastic cover or prismatic features that disperses the light as it passes through the cover. However, such a semi-transparent cover or prismatic structured cover absorbs a significant amount of light, thereby reducing the overall lumen/watt efficiency of the LED light tube.
Heat dissipation from the LEDs is another problem in the conventional LED light tube. In the conventional LED light tube 100, the heat generated at the LEDs 101 is dissipated away from the LEDs 100 through the PCB 103 to the grooves 121 of the aluminum tube cover 105 as shown in FIG. 2. From the aluminum tube cover 105, as well as the plastic tube cover 107, the heat is dissipated by means of external convection. Since the heat dissipation path from the LEDs to the aluminum tube cover 105 is long, the efficiency of the heat dissipation in the conventional LED light tube is not sufficient.
Further, a driver circuit 109 for the LEDs of the conventional LED light tube typically includes a switched mode power supply (SMPS) with an AC to DC conversion function at high frequency and with a low voltage output, together with other components. As such, the size of the driver circuit 109 in the conventional LED light tube becomes so large that it has to be located in a space between the PCB 103 and the aluminum cover tube 105 (see, FIG. 2). Since the driver circuit 109 is located under the PCB 103, a half of the tube is not effectively utilized.
Accordingly, there is a need for an LED light tube which can suppress the uncomfortable glare and obtain better heat dissipation efficiency, which overcomes one or more of the foregoing problems.